1. Field of the Invention
The present invention relates to a control system for a prime mover and a hydraulic pump of a hydraulic construction machine, and more particularly to a control system for a prime mover and a hydraulic pump of a hydraulic construction machine, such as a hydraulic excavator, wherein hydraulic actuators are operated by a hydraulic fluid delivered from a hydraulic pump, which is driven by an engine for rotation, for carrying out works required.
2. Description of the Prior Art
Generally, in the hydraulic construction machine such as a hydraulic excavator, a diesel engine is provided as a prime mover, at least one variable displacement hydraulic pump is driven by the diesel engine for rotation, and a plurality of hydraulic actuators are operated by a hydraulic fluid delivered from the hydraulic pump for carrying out works required. The diesel engine is provided with input means, such as an accelerator lever, for instructing a target revolution speed. An amount of fuel injected is controlled depending on the target revolution speed, and an engine revolution speed is controlled correspondingly.
In relation to control of the prime mover and the hydraulic pump in such a hydraulic construction machine, there are known several prior arts. For control of the hydraulic pump, JP, A, 3-189405, for example, discloses a positive pump tilting control system wherein a target tilting position of a hydraulic pump is calculated depending on the direction and input amount in and by which control levers or pedals of operation instructing means respectively associated with a plurality of hydraulic actuators are each operated, to thereby control an actual tilting position of the hydraulic pump.
For control of the prime mover, a control system is proposed in JP, A, 7-119506 entitled Revolution Speed Control System for Prime Mover of Hydraulic Construction Machine. In the disclosed control system, a target revolution speed is input, as a reference, by operating a fuel lever, and the direction and input amount in and by which control levers or pedals of operation instructing means respectively associated with a plurality of hydraulic actuators are each operated (hereinafter referred to simply as the lever operating direction and lever input amount), as well as an actuator load (pump delivery pressure) are detected. A modification value of the engine revolution speed is determined based on the lever operating direction, the lever input amount and the actuator load, and the target revolution speed is modified using the revolution speed modification value to thereby control the engine revolution speed. In this control system, when the lever input amount is small and when the actuator load is low, the engine target revolution speed is set to a relatively low value for energy saving. When the lever input amount is large and when the actuator load is high, the engine target revolution speed is set to a relatively high value for increasing working efficiency.
Further, JP, A, 62-94622 discloses a control system which receives a signal of the lever input amount and controls both a prime mover and a hydraulic pump in a linked manner. In the disclosed control system, a hydraulic flow rate necessary for work is calculated from the input amount by which a working mechanism control lever is operated, and at least one of a revolution speed of an engine and a tilting angle of a variable pump driven by the engine is controlled in accordance with a resulting control signal, for thereby improving fuel consumption during the operation under a light load and a low flow rate, and reducing a noise level. Additionally, when an actual engine revolution speed is lower than a target engine revolution speed, the pump tilting is reduced to prevent the engine from stalling.